Why does Guinness hit differently?

I (m32) have been drinking for quite some time, ex hospitality, grew up in Magaluf etc. I often drink different types of alcohol with varying degrees of drunkiness depending on what I drink. However, guiness has and will always be my safety drink. I’ve just sank my 8th pint (in a 4 hour period) and feel fine. 4 rums though and I’d be chatting rubbish to anyone. Why is this!?